Equipotential cathode vacuum tube



Oct. 9,'A 1928.

R. s. oHL EUIPOTENTIAL CATHODEl VACUUM TUBE Filed Nov; 1'8.- 1924 alwwl?INVENTR I' 35. o@

ATroRNgy Patented Oct, 9, 1928-.

UNITED STATES PATENT OFFICE. l'

RUSSELL S. OHL, OF NEW YORK,` N. Y., ASSIGNOR TO AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

EQUIZPOTENTIAL CATTHODE VACUUM TUBE.

Application filed November 18, 1924. Serial-No. 750,642.

This invention relates to equi-potential cathode vacuum tubes andparticularly to means for preventing the electrons created by theheating element per se of tubes of that ltype from interfering with thenormal anodecathode `current of such tubes.

In vacuum tubes in which the cathode is heated by the conduction ofcurrent therethrough, there is, of course, a difference of potentialbetween the terminals of the cathode, which difference of potentialproduces a detrimental effect in the operation of the tube. To eliminatethis effect, there has been developed the so-called equi-potentialcathode tube which is characterized by the fact that substantially allpoints of the cathode are at the same potential. In tubes of this typethe cathode is rendered active by means external to the cathode itself.This means, which may be termed the heating element of the tube, mayoperate in various ways in order to produce the desired effect, viz,rendering the cathode electron-emitting. Among the possible ways aredirect radiation of heat from the heating yelement tothe cathode orbombarding the cathode with electrons so as to render it in turnelectron-emitting.

My invention relates to tubes in which the cathode is rendered active bythe radiation of heat from the heating element. As is well known,electrons are emitted tosome extent even in vtubes ofthe equi-potentialcathode type, which depend upon the principle of radiation of heat torender' the cathode active.v If the source for energizing the heatingelement is of the alternating current type, electrons will be emittedfrom the heating ele- 'ment at a varying rate, depending upon the cyclicreversals of the alternating current. These electrons will tend to flowto the plate and the grid of the vacuum tube, together with theelectrons that flow directly from the equi-potential cathode itself,andwill produce a variation in the output current of the said tube which,for example, in a radio receiving apparatus, will produce a hum in thesound producing device, such as a telephone receiver er loud-speaker.

It is the object of this invention to provide means for the substantialelimination of electron emission from the heating element itself.

This invention will be. clearly understood from the iollowingdescription'when read in connection wlth the attached drawing, in

which Figure 1 shows schematically a form of embodiment of the'invention in which the electrons created by the heating element aredriven back to that element; land Fig. 2 shows means for attracting suchelectrons to the cathode itself. Y

The input circuit of Fig. 1 is coupled to the input side of the vacuumtube circuit by means of the transformer 1. This input circuit maybeconnected With an antenna circuit either directly. or through otherapparatus. The vacuum tube 2 comprises a grid 3, a plate 4, anequi-potential cathode 5, and a heating element 6. The cathode 5 isconnected with the midpoint of the secondary Winding of the transformer1, of which oneof the outer terminals is connected with the grid 3, andthe other outer' terminal is connected through the condenser 7 with theplate 4 of the tube.

This condenser is intended to balance the ca-` v winding of which isconnected with a. source of alternating current. A rheostat 13 isinserted in series with the heating element to control the degree ofheat. Connected between the midpoint of the winding 14 and the cathode 5is a battery 15, the positive pole of which should -be toward' theheating element.

The manner in which this invention functions to obtain the desiredresult isas follows: lVhen the alternating current energy is applied tothe heating element 6 in order to produce heat therein, which in turnwill heat the cathode 5 and render the latter electroneinitting,electrons would also be emitted to a varying extent from the heatinglelement 6. There would be a tendency for these electrons to travel tothe plate and the grid 3 of the tube, and since they result from analternating current, the number of electrons would vary with the cyclicreversals of curmeans of the battery 15. This battery keeps the heatingelement 6 at such a positive potential with respect to the cathode ofthe tube that the tendency forthe electrons to leave the heating elementis checked. This, of course, results in quiet operation of the tube.

The arrangement shown in Fig. 1 is based upon the principle of keepingthe cathode `negative with respect tothe heating element so thatelectrons created by the heating element per se Will be prevented fromescaping therefrom, and thus any interference with the normalanode-'cathode current isprevented. An alternative arrangement is shownin Fig. 2 in which the same reference vnumerals have been used toindicate similar parts. In this arrangement the battery 16, which inposition corresponds to the battery 15 of Fig. 1, is so poled as to makethe cathode 5 -posit-ive with respect to the heating element 6. As thusarranged, any electrons created by the heating element 6 will be drawnto the cathode 5 which is in close juxtaposition thereto, and

thus are prevented from traveling to the other electrodes of the tubeand causing interference with the normal space current. Thearrangementshown 'in this figure is particularly well adapted for useinconnection with equi-potential cathode tubes in which the cathode tubesof that type there would normally be a tendency for electrons to escapefrom the heating element and to pass through the open top of the cathodeto the other electrodes of' the tube. By employing an arrangement lsimilar to vthat shown in Fig. 2, the positive charge upon thecylindrical cathode tends to draw to .1t any electrons that may be freedfrom the heating element.A i

The arrangements shown in the liguresand 7 described herein are simplyillustrative of the invention. It will, of course, be obvious thathaving a cathode and means separate therefrom tov heat the said cathode.of polarizing means connected betweenv said -cathode and said heatingmeans to substantially prevent the radlatlon of electrons from the saidheat ing means.

2. In a vacuum tube', the combination with ment to the cathode. consistsof a cylinder open at the top. With combination with a vacuum tu acathode to emit electrons when heated of a heating element to energizethe said cathode, a plate, an evacuated vessel enclosing all of theaforesaid elements, means for energizing the said heating element, andpolarizing means connected between said cathode and said heating elementto substantially prevent the emission of electrons from the said heatingelement to the cathode.

3. The combination with a vacuum tube having an evacuated vesselenclosing a cathode, a plate, a grid,'andv a heating element to renderthe said cathode active, means to energize the said heating element, acircuit having a source of potential connecting the said plate and saidcathode, a second source of potential connected vbetween the saidheating element negative side to the saidcathode to prevent v theradiation of electrons from theheating element.

5. In an electrical translating systemthe combination with a vacuum tubehaving an anode, a cathode, and a heating element adjacent to the saidcathode to activate the latter by direct radiation, of a source ofalternating current to energize the Said heating element,

and means to substantially prevent the emisv sion of electrons from thesaid heating ele- 6. In an electricv translatingy system employing avacuum tube having an anode, a uni- .potential cathode, and a heatingelement adj acent to the said cathode to activate the latter, the methodof preventing detrimental elects in the anode circuit by electronsproduced by the energization of the said heating element, whlchvconsists in applying a potential between the heating element and thesaid cathode to substantially prevent the emission of the said electronsto the cathode.

7. In an electric translating system employying a vacuumgtube having ananode, a unipotential cathode, and a heating element adj acent to thesaid cathode to activate the latter,

' the method of preventing detrimental effects inthe anode circuit byelectrons produced by the'energization of the said heating element,which consists in lapplying a potential between the said heatingelementand the said cathode, the said potential being so polarized the heatingelement to the cathode.

8.. In an electrical translating s stem, the

aving an as to prevent the emissionof electrons from anode, a cathode, aheating element adjacent to the said cathode, of a source of alternatingcurrent connected with the said heating element to energize the latterwhereby the Said cathode is activated, and a Source of direct currentpotential connected between the said heating element and the saidcathode, the said source being of such magnitude and' so poled as toprevent electronic emission from the said heating element to thecathode.

In testimony whereof, I have signed my name to this speciication this17th day of November, 1924.

RUSSELL S. OHL.

